Swept Volume Theory

Discussion in 'Hydrodynamics and Aerodynamics' started by Sailor Al, Aug 2, 2022.

  1. Sailor Al
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    Sailor Al Senior Member

    I think you are confusing the messenger with the message. Shooting the messenger doesn't change the message.
     
  2. tlouth7
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    tlouth7 Senior Member

    This is the first I have seen of that article. Upsettingly I was taught thermofluids by one of the quoted experts. Either their words were misconstrued by the journalist or they were hamming it up for the article. We devoted a big chunk of a lecture specifically to dismantling the exact myth perpetuated by this article! I would like to apply Hanlon's razor here but I struggle to do so.

    The only good parts of the article are the third paragraph where they say that we do have good models for lift, and the section that talks about a "reciprocal cause and effect relationship". Curved streamlines imply non-uniform pressure distributions, and are driven by those distributions. This reciprocity of cause and effect is why the governing formulae are differential equations with no analytical solutions*, and why we turn to numerical methods (CFD) to find equilibrium results.

    *This sentence is of course a gross simplification.

    I have just reread the post in the original, and honestly I take no issue with it. The problem seems to be that we are all hung up on OP's insistence that this will somehow overturn all that comes before, rather than simply being a reframing of existing principles.
     
  3. Sailor Al
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    Sailor Al Senior Member

    And interestingly, that precisely one of the statements with which I have a serious disagreement, but we're not here to critique the SciAm article.
    That has to be one of the most lukewarm of expressions of support , but I welcome it nevertheless.
    And there I think you have hit the nail on the head.
    Certainly I made that claim in my initial post, but it doesn't actually appear in the article itself. I guess I inserted it to gather some attention. It certainly is not a part of the theory, essential or otherwise.
    What is interesting is that none of the dozen or so objections that have been raised in the six threads in which I have engaged over the past three days have been objections to the theory itself. They have been to the answers I have given to the questions* that I thought up to go in the Appendix. So it seems that the theory itself remains unchallenged which I think is a good sign.
    * Plus a few trolling comments aimed at me individually. I learned a hard lesson last year on this forum, that posts should relate to the material not the member posting. Other members of the forum haven't learned to play the ball not the man (and we know who they are!).
    If I had the time, money, desire, and an international court, I'm pretty sure I could mount a successful defamation case against them.
     
  4. Skyak
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    Skyak Senior Member

    That article is clickbait garbage. The premise that "No one can explain why planes stay in the air" is lie. They start with this lie (ancient Greeks called the fallacy "begging the question") because it makes people read the article, which makes them money! Your acceptance and attraction to this lie tell me you don't know anything about the topic and you will accept any premise that implies you are smarter than highly educated people.

    There is no paradox. Classical mechanics still apply if you know how, and no amount of theory will displace the ignorance of someone who's intent is not to learn.

    I am sure that you think my response is rude and uncalled for -let me explain. I understand aerodynamics and it is in large part thanks to Prof Drela's Aerodynamics 101 (available to audit free through Ed-X). Take that class and you will see he explains very thoroughly how planes fly and never needs any of the misapplied crap offered in that SA article. You will realize you were duped and owe an apology to educated people that have been insulted.
     
  5. gonzo
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    gonzo Senior Member

    The Wright brothers invented the wind tunnel to be able to see the behavior of the air flow. By now, there are thousands of videos online showing wind tunnels experiments. Sailor Al makes statements like:
    , when referring to the article where it says that we have good models for lift. Either he is deliberately obtuse, or has never seen a flying airplane. Airplanes are designed based on those models :rolleyes:
     
  6. tlouth7
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    tlouth7 Senior Member

    Very well:

    This theory appears to be nothing more than a restating of the standard momentum/Newtonian argument in a different reference frame. The only reason the air cannot simply move out of the way of the front side, and move in to fill the space on the back side, is that this requires a change of momentum which is driven by a pressure differential. You can include those effects in your theory but then you have nothing new, or you can ignore them but then you have no mechanism for your low and high pressures on the sail.
     
  7. Sailor Al
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    Sailor Al Senior Member

    It's not clear to me why you have introduced this as part of a critical review of the theory, perhaps you could assist by putting it in the context of a review of the theory itself.
     
  8. Sailor Al
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    Sailor Al Senior Member

    I wonder if you would be kind enough to point out the text of the SciAm article which you contend contains a lie, and then explain, with references, the basis of your fairly serious accusation of lying on the part of the author?
     
  9. Sailor Al
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    Sailor Al Senior Member

    And I wonder if you could post a link to that document?
     
  10. Sailor Al
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    Sailor Al Senior Member

    According to many authoritative sources including Franklin Institute:
    'In the Fall of 1901, the Wright Brother decided to begin a "series of experiments to accurately determine the amount and direction of the pressure produced on curved surfaces when acted upon by winds at the various angles from zero to ninety degrees." to measure the effect of changes to their wing shape on the lift and L/D ratio.'

    Note: "...amount and direction of pressure..." (my emphasis).

    This may seem to be nit-picking, but it goes to the heart of my thesis that the source of this pressure is inadequately explained in the literature.

    Actually neither.
     
  11. Sailor Al
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    Sailor Al Senior Member

    I suspect that's a thinly veiled jab at me. If so, I think it would not be unreasonable to request it be either withdrawn or supported with evidence.
    If not then I'm not sure what purpose it served.
     
  12. tlouth7
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    tlouth7 Senior Member

    Your theory is that as the sail moves forward relative to the air it creates a gap, and that this results in a low pressure region. But that gap can simply be instantly filled with air from nearby, at which point there would be no low pressure region at all! So you need a mechanism to prevent air instantly rushing into the space left behind the sail, do you have such a mechanism?
     
  13. Sailor Al
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    Sailor Al Senior Member

    Thank you for your thoughtful enquiry.
    Please review the text supporting Fig. 14 which explains the creation of the low pressure using the model of bubbles.
    And as you probably know, in nature, nothing happens "instantly". The question of the actual rate of the redistribution of pressure is addressed in "Unanswered Questions".
     
  14. tlouth7
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    tlouth7 Senior Member

    So you rely on existing Newtonian mechanics to cause this low pressure region (and the corresponding high pressure region on the front side)? If so this theory is exactly the Newtonian momentum based explanation which you claim was debunked by the SciAm article. It makes no difference whether the sail moves forward and the air rushes in behind it, or the air flows past the sail and changes momentum in order to curve round behind it. As you state in the article, inertial reference frames are equivalent.
     

  15. Sailor Al
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    Sailor Al Senior Member

    Once again, you are introducing novel concepts to your critical review of the theory. Nowhere does it rely on Newtonian force or momentum to explain the low pressure.
    Could you provide a link to this "Newtonian momentum based explanation" so at least we can compare apples with apples. There are so many versions.
    No, I did not claim that the SciAm article debunked any theory. You are misquoting me. Here is my quote:
     
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